Choosing an enlarger.

This is the most important tool in the darkroom after the enlarging lens. With this in mind you need to consider the following: 

1.   The number of negative sizes you may wish to print. It is a good idea to get a multi format enlarger even if you are only going to use 35mm.

2.   The most appropriate lens size and quality.

3.   What type of negative illumination. Diffuser or Condenser.

4.   The maximum size of print you are likely to make.

5.   Whether you may want to do colour at a later date. Colour headed enlargers can be used with multigrade papers. 

As mentioned in “3” the type of negative illumination you choose is worth  a lot of consideration -  there are positive and negative points to both. Here are some of the pros and cons: 

Diffuser enlarger: 

Diffuser light box

This type of enlarger design is used with colour and multigrade heads. The light travels through a mixing box and semitransparent screen above the negative. To counteract the drop off in light, these enlargers use a powerful quartz-iodide bulb.  This multi directional light passes through the negative and down to the paper. The affect of this will produce a gentler, softer quality to the  light, producing a less contrasty grade for grade photograph. As a result damaged and flawed negatives lose or soften some of their faults. 

There are tonal differences between diffuser and condenser produced photographs because of the way light passes around the silver particle's. This is negated when using Chromogenic monochrome and colour films as they rely on dyes to capture the light. 

Condenser enlarger: 

Condenser light box

Uses a plano-convex lens which spreads a bright hard illumination  evenly across the negative. Supplied from a opal tungsten lamp. The harshness of this light produces a contrast enhancement that appears to make  fine detail more exaggerated. This crisp appearance to the photograph has the negative affect of bringing into sharp focus the grain, any scratches, flaws and dust from the negative, meaning more time spent on retouching. These enlargers are subject to the Callier affect this is where the highlights in the negative scatter the light more than the shadow areas creating the increase  in contrast.

Enlarging len which aperture?

The quality of your enlarging lens will lead to better and sharper results at greater magnification. The aperture ( low number = large opening, high number = small opening) you set not only affects the amount of light it lets through but the depth of field as well. A good average aperture is F/5.6 in most cases. If the exposure times are to short a larger F number is needed, this will give you a chance to hold back shadow areas that may become to dark to show any detail. But don't get carried away and close down the lens by too  many F numbers as this may over heat the negative causing it to buckle, making the picture loose sharpness.